The present invention pertains to optical communications. More particularly, this invention relates to an optical multiplexing device which spatially combines multi-wavelength light from a plurality of lasers into an optical fiber. In certain preferred embodiments, the improved multiplexing device of the present invention is particularly suited for wavelength division multiplexing systems for the fiber-optic data-communications and telecommunications systems.
In prior art wavelength division multiplexed optical communication systems, many different optical wavelength carriers provide independent communication channels in a single optical fiber. Future computation and communication systems place ever-increasing demands upon communication link bandwidth. It is generally known that optical fibers offer much higher bandwidth than conventional coaxial communications; furthermore a single optical channel in a fiber waveguide uses a small fraction of the available bandwidth of the fiber (typically a few GHz out of several tens of THz). By transmitting several channels at different optical wavelengths into a fiber (i.e., wavelength division multiplexing, or WDM), this bandwidth may be more efficiently utilized.
Prior art optical multiplexing devices combine or separate multiple light signals with varying optical wavelengths. Such optical multiplexing devices have applications for both dense and course wavelength division multiplexing (DWDM & CWDM) for both multi-mode and signal-mode fiber optic data communications and telecommunications. Multiple wave-length light sources are combined into a single optical path for transmission.
The prior art includes inherent problems overcome by the present invention. Prior art wavelength division multiplexed (WDM) devices are typically designed using dielectric filters requiring alignment or expensive waveguides. The combiner/WDM device described herein utilizes plastic-mold injection to create a compact device capable of combining multiple optical signals into a single optical fiber, and which avoids the use of dielectric filters and the use of expensive waveguides. While a single molded device can be constructed to create one embodiment of the present invention, two or more parts can be combined to accomplish the same function, and may be necessary to achieve certain environmental conditions.
The prior art also includes an optical power combiner which utilizes collimators and a focusing lens to concentrate multiple output beams to increase power density; see Lee et al U.S. Pat. No. 5,377,287. The Lee et al device combines the outputs of, for example, 19 passive optical fibers arranged concentrically together with 19 collimating lenses and a Fresnel focusing lens. The Lee et al design does not achieve isolation from unwanted reflections or a uniform coupling efficiency between each fiber optic input and the single output. The present invention, in contrast, uses a separate radial sector of the focusing lens to focus each separate laser output. Each laser output beam of the present invention therefore has the same degree of refraction as it passes through the focusing lens; this feature simultaneously creates a uniform coupling efficiency (as shown below) and prevents unwanted reflections back through the optical pathway to the input lasers. Furthermore, the Lee et al combiner does not multiplex n different wavelength channels, as does the present invention. Therefore, for the above reasons, the Lee et al combiner simply is not effective for communication purposes, which is the primary purpose of the present invention.
The present invention provides, for the first time, an inexpensive, injection molded, one piece optical combiner capable of combining, separately collimating and focusing the output of multiple lasers into a single optical fiber with a uniform, high coupling efficiency. The invention includes optional passive alignment pins molded into the combiner. An optional two piece combiner is also provided for use in certain environments. For example, the invention in one embodiment combines the output of four lasers arranged in a two dimensional, two by two array into a single fiber.
One of the key objects of the present invention is to provide a compact and cost effective optical combiner for both single-mode or multimode fiber optic communication systems, all without requiring the use of dielectric filters and the alignment necessitated by those filters or expensive waveguides.
Another object of the present invention is to minimize optical loss due to divergence of light between the source coupling optics and the fiber optic connector coupling optics.
Another object of the present invention is to minimize reflections directly back to the same focal position from which they were emitted.
A further object is to provide an optical combiner wherein a single focusing lens is utilized to uniformly and efficiently combine n separate wavelength channels by passing each channel through a separate radial sector of the focusing lens.
Another object of the present invention is to integrate a fiber optic connector within the optical module, to passively align an optical fiber to the coupling optic.
Further objects and advantages will become apparent from the following description and drawings.